How to Dual-Boot Linux and Windows 11: A Safe Step-by-Step Guide

Messing with partitions feels like the kind of thing that ends with “and now nothing boots.” It doesn’t have to. Do it in the right order: shrink first, back up first, install alongside instead of over. Then Ubuntu sits next to your existing Windows 11 setup and a boot menu normally lets you pick your OS at power-on. The alongside option is designed to keep your Windows files, installed Windows apps, and license in place, but any partition change carries some risk, which is why the backup comes first. (Windows programs still run only in Windows, not in Ubuntu.)

What Is Dual-Booting?

Dual-booting means two separate operating systems live on the same drive in their own partitions, and a boot loader (Ubuntu uses one called GRUB) lets you pick between them at startup. It’s different from a virtual machine, where Linux runs inside a window on top of Windows. A dual-boot install runs Ubuntu natively, with full access to your CPU, GPU, and RAM. The tradeoff: setup touches your disk partitions and boot configuration, so a few prep steps matter more here than in a typical software install.

Prerequisites

Confirm these before you start:

• A Windows 11 PC with UEFI firmware (Windows 11 itself requires UEFI, so a PC that meets its requirements already has it; legacy BIOS-only machines need a different process not covered here)
• Free space on your C: drive for Ubuntu: Ubuntu’s tutorial lists at least 25 GB of storage, but we suggest 50–100 GB if you’ll use Ubuntu regularly, and more if you’ll keep large files or games there
• A USB flash drive of 12 GB or larger that you can erase completely
• An external hard drive or cloud storage account for a full backup
• Administrator access to Windows to reach Disk Management, Power Options, and BitLocker settings
• An internet connection to download the multi-gigabyte Ubuntu ISO (size varies by release; a wired Ethernet connection is often faster and steadier than Wi-Fi for this)

Requirement	Details
Device	Windows 11 PC with UEFI firmware
OS version	A currently supported Windows 11 version
Free disk space	25 GB minimum per Ubuntu’s tutorial; 50–100 GB recommended for practical use
USB drive	12 GB or larger, will be erased
Backup destination	External drive or cloud storage

Check your current Windows edition and build first: Settings > System > About. You’ll want this information handy if you ever need to contact support.

Step-by-Step Guide

Step 1: Back Up Your Files

Partition changes are generally safe, but “generally” isn’t good enough when the alternative is losing family photos or years of documents. Copy anything irreplaceable to an external SSD, an external hard drive, or a cloud service like OneDrive before you touch Disk Management.

• Connect an external drive or open your cloud storage app.
• Copy your Documents, Pictures, Desktop, and any project folders you can’t afford to lose.
• Verify the copy by opening a few files directly from the backup location.
• For the strongest safety net, also make a full system image of the drive with a disk-imaging tool and store it on an external drive. Pick a tool that can also create bootable recovery media, so you can restore the image even if Windows won’t start. Windows Backup (in Settings > Accounts > Windows backup) mainly syncs selected folders, settings, and app lists to OneDrive; it isn’t a full disk image, so don’t rely on it alone before repartitioning.

Tip: If you lose power mid-shrink or mid-install, a fresh backup is the difference between a minor annoyance and a bad day. If you’re working on a desktop, plugging into a UPS during this process protects against exactly that scenario.

Step 2: Back Up Your BitLocker Key, Then Turn BitLocker Off

Resizing a partition or changing boot settings can trigger Windows to demand your BitLocker recovery key on the next startup. Skip this step and you risk getting locked out of Windows entirely: no key, no way back in.

• Search Windows for Manage BitLocker and open it.
• Check whether BitLocker is On for your C: drive.
• If it’s on, click Back up your recovery key and save it to your Microsoft account, a printed copy, or a USB drive that isn’t the one you’ll use for Ubuntu.
• Write down or photograph the 48-digit recovery key somewhere you can access without your PC.

Saving the key isn’t enough on its own. Ubuntu’s documentation says that when BitLocker is on, the encrypted Windows content isn’t readable to the installer, so it can’t install alongside Windows without data loss, and its guide to turning off BitLocker says disabling it might be necessary first. Recent Ubuntu installers handle some BitLocker setups better, but whether yours can depends on your disk layout. The safest path is to turn BitLocker off before you continue, and to follow any BitLocker message the installer shows:

• If your PC uses Device encryption (common on Windows 11 Home), open Settings > Privacy & security > Device encryption and turn it Off. If you have full BitLocker (Pro, Enterprise, and Education), go to Control Panel > System and Security > BitLocker Drive Encryption and click Turn off BitLocker. Menu labels can vary slightly by Windows version.
• Wait until Windows reports that decryption is complete. This can take a while on a large drive; keep the PC plugged in.
• Restart Windows once and confirm Manage BitLocker shows the drive as off before moving on.

Warning: Ubuntu notes that some Windows versions won’t let you re-enable BitLocker after you disable it. If you plan to re-encrypt Windows afterward, check that your edition supports it. If the status says “BitLocker waiting for activation,” Ubuntu’s guide explains that BitLocker is enabled but your data isn’t encrypted yet, and tells you to click Turn on BitLocker first; follow its steps from there.

Step 3: Shrink the Windows Partition With Disk Management

Ubuntu needs its own unallocated space to install into. Windows’ built-in Disk Management tool handles this without any third-party software.

• Right-click Start and select Disk Management, or press Win + R, type diskmgmt.msc, and press Enter.
• Find your C: partition in the list.

• Right-click the C: partition and select Shrink Volume.
• In the Enter the amount of space to shrink in MB field, type how much space to free up. For a typical Ubuntu install, enter 51200 for 50 GB or 102400 for 100 GB.
• Click Shrink.

• Confirm a new block labeled Unallocated appears next to your C: partition. Leave it unallocated; don’t format it or assign a drive letter. Ubuntu’s installer handles that later.

How much space do I need? Ubuntu’s install tutorial lists at least 25 GB of storage. That’s a floor, not a comfortable size: 50–100 GB leaves room for updates, swap, apps, and personal files.

Step 4: Turn Off Fast Startup

Fast Startup hibernates core parts of Windows on shutdown instead of fully powering down. Writing to a hibernated or uncleanly closed Windows volume from Linux risks file system errors, so turn it off. If you use Hibernate separately, always choose Shut down in Windows (not Hibernate) before booting Ubuntu.

• Open Control Panel > Hardware and Sound > Power Options.
• Click Choose what the power buttons do in the left sidebar.
• Click Change settings that are currently unavailable (requires admin rights).
• Uncheck Turn on fast startup (recommended).

• Click Save changes.
• Fully shut down the PC (not restart) at least once before continuing; this clears any existing hibernation state.

Step 5: Leave Secure Boot On (Usually)

Older Linux guides tell you to disable Secure Boot in the UEFI firmware. Skip that advice. Current Ubuntu Desktop releases ship with a signed boot loader that normally works with Secure Boot enabled. Leave it on by default. If the USB is refused with a Secure Boot or security violation message, first update your PC’s firmware and re-check the ISO checksum; turning Secure Boot off temporarily is a last resort, and some third-party drivers (such as NVIDIA’s) may ask you to enroll a key during installation.

• If you want to confirm Secure Boot is on, go to Settings > Privacy & security > Windows Security > Device security > Core isolation details, or check System Information (msinfo32) for the Secure Boot State field.
• Leave the setting as-is. No firmware changes are needed for a standard Ubuntu install.

Step 6: Create a Bootable Ubuntu USB Drive

• Go to the official Ubuntu Desktop download page and grab the current LTS release (Ubuntu 26.04.1 LTS at the time of writing) for 64-bit PCs. Before writing it to USB, check the file against Ubuntu’s published SHA256 checksum (Ubuntu’s verification guide explains how). In Windows PowerShell, Get-FileHash .\<iso-file-name>.iso prints the hash to compare.

• Download and install a USB imaging tool such as Rufus (Windows-native, no install required) or balenaEtcher.
• Plug in your 12 GB+ USB drive; everything on it will be erased.
• Open Rufus, select your USB drive under Device, and select the Ubuntu ISO you downloaded under Boot selection.
• Leave the partition scheme as GPT and target system as UEFI (non CSM); this matches the standard UEFI setup on modern Windows 11 PCs.
• Click Start and wait for the write process to finish; how long it takes depends on your USB drive and PC.

Step 7: Boot From the USB Drive

• Restart your PC with the USB drive still plugged in.
• As it restarts, repeatedly press your manufacturer’s one-time boot menu key, commonly F12, F10, Esc, or Del (check your PC’s manual if none of these work).
• Select the USB drive entry. If you see two entries for the same drive, choose the one labeled UEFI; the other is a legacy BIOS entry that can cause the “alongside Windows” option to disappear later.
• Wait for the Ubuntu boot screen, then select Try or Install Ubuntu.

Intel RST or VMD alert? Some PCs, especially laptops, use Intel Rapid Storage Technology (RST/VMD) for the drive. Ubuntu’s install tutorial says RST isn’t supported and you can’t continue until it’s disabled in the firmware. Don’t just flip the firmware setting to AHCI: Windows can fail to boot if its storage driver isn’t prepared first. Ubuntu’s RST help page (help.ubuntu.com/rst) describes preparing Windows to boot in AHCI mode first and then changing the firmware setting, and some PC makers publish their own steps. Stop, follow those instructions in that order, and make sure your backup and BitLocker key from Steps 1 and 2 are ready before changing anything.

Step 8: Install Ubuntu Alongside Windows

• Choose Install Ubuntu, then follow the prompts for language, keyboard layout, and network. Connecting is optional, but it lets the installer fetch updates and drivers; you can also install offline.
• Choose Interactive installation, then Default selection (you can add apps later).
• When offered, check the boxes to install third-party software for graphics and Wi-Fi hardware and for additional media formats; this saves you a driver hunt later.
• On the installation type screen, select Install Ubuntu alongside Windows Boot Manager. Make sure the right drive is selected, then use the slider to set Ubuntu’s space. This option is designed to preserve existing files, but only if you pick the correct disk and check the summary before installing.

Warning: Never select Erase disk and install Ubuntu. That option deletes every partition on the drive, including Windows and all your files.

• Skip the optional disk-encryption choices unless you want them. If you do choose Ubuntu’s LVM, ZFS, or TPM-backed encryption, you’ll get a separate security or recovery key for Ubuntu. Store it outside the PC, alongside your Windows BitLocker key, because you can’t recover your Ubuntu data without it.
• Create your name, computer name, username, and password, then choose your time zone.
• Review the summary screen carefully: it should show Ubuntu going into the free space on the correct disk and no Windows partition being formatted. Then click Install.
• Wait for the installation to finish; the time depends on your hardware and whether the installer is downloading updates.
• When prompted, click Restart Now, then remove the USB drive when Ubuntu tells you to and press Enter.

Step 9: Understand the GRUB Boot Menu

After the restart, you’ll see a black text screen instead of the usual Windows logo. That’s normal, not an error. It’s called GRUB (GRand Unified Bootloader), and it lists your available operating systems.

• Use the arrow keys to highlight Ubuntu or Windows Boot Manager.
• Press Enter to boot into your selection.
• If you do nothing, GRUB normally boots the highlighted default (Ubuntu on a standard install) after a short countdown; the exact timeout depends on your configuration.

On a typical dual-boot install this menu shows on every restart, and that’s how you switch between the two operating systems. Exact entry names can differ by PC and installer version. If your PC boots straight into Windows instead, the firmware boot order needs changing; see the troubleshooting section below.

Configuration: Adjusting GRUB’s Behavior

A few settings are worth knowing once you’re up and running:

• Change the default OS: From inside Ubuntu, back up the file first (sudo cp /etc/default/grub /etc/default/grub.bak), then edit /etc/default/grub and set GRUB_DEFAULT to the exact menu entry title in quotes (for example “Windows Boot Manager (on /dev/nvme0n1p1)”, copied from your GRUB menu) rather than a number, since numbered positions can shift after kernel updates. To see the exact titles, run grep -E "^\s*(menuentry|submenu)" /boot/grub/grub.cfg; an entry nested inside a submenu needs the form “Submenu title>Entry title”. Run sudo update-grub to apply it.
• Change the timeout: The same file has a GRUB_TIMEOUT value (in seconds) controlling how long the menu waits before auto-booting.
• Force the boot menu to always show: Set GRUB_TIMEOUT_STYLE=menu if the menu is skipping past too quickly to read.

Run this command in an Ubuntu terminal after editing the file:

sudo update-grub

Tips and Troubleshooting

Windows Disappeared From the Boot Menu

Why it happens: GRUB sometimes fails to detect the Windows Boot Manager entry correctly, or the firmware’s boot order changed during installation.

Fix: Boot into Ubuntu and run the update command to refresh GRUB’s OS list:

sudo update-grub

Restart afterward. If GRUB simply missed the Windows entry, it should reappear. update-grub won’t fix a missing or damaged firmware boot entry, a Windows bootloader problem, or a drive Ubuntu can’t read because of BitLocker or RST. If Windows still doesn’t appear, restart and open your firmware’s one-time boot menu (F12/F10/Esc at startup) to check whether Windows Boot Manager still exists as a boot option there. Don’t delete or recreate the Windows Boot Manager entry. The underlying boot files are still on the EFI System Partition; GRUB just needs to find them.

The Installer Only Offers “Erase Disk”

Why it happens: The installer didn’t detect free unallocated space, often because the shrink didn’t complete or you’re using an unusual partition layout.

Fix: Don’t proceed. Reboot into Windows, reopen diskmgmt.msc, and confirm you see a block labeled Unallocated next to C:. If it’s missing, repeat Step 3. Retry the Ubuntu installer once the unallocated space is confirmed.

The Installer Won’t Continue or Freezes

Why it happens: Common culprits are BitLocker still active (or not fully decrypted), Intel RST/VMD storage mode, Fast Startup leaving Windows partially hibernated, or the USB booted in legacy BIOS mode instead of UEFI.

Fix: Cancel the install and boot back into Windows. Confirm BitLocker or Device encryption is fully off (Step 2), double-check Fast Startup is off, then fully shut down (not restart). If the installer showed an RST alert, follow the RST note in Step 7. Re-enter the boot menu and pick the UEFI-labeled USB entry.

BitLocker Asks for the Recovery Key After Installing Ubuntu

Why it happens: Changing partitions or firmware settings can trip BitLocker’s tamper detection. That’s a security feature doing its job, not a sign something broke.

Fix: Enter the recovery key you saved in Step 2. Once Windows boots, reopen Manage BitLocker to confirm protection status. It can also appear later if you turned BitLocker back on after installing Ubuntu and then changed boot or firmware settings.

The PC Boots Straight to Windows, No GRUB Menu

Why it happens: Firmware boot order defaults to Windows Boot Manager instead of GRUB.

Fix: Open the firmware boot menu at startup and manually select ubuntu once. If you want GRUB to load by default every time, go into your UEFI firmware settings and move the “ubuntu” boot entry above “Windows Boot Manager” in the boot order list.

Wrapping Up

Back up, turn off BitLocker, shrink the partition, disable Fast Startup, and pick Install Ubuntu alongside Windows Boot Manager. After that, every restart is just picking an OS from the GRUB menu. If Windows vanishes from that menu, start with sudo update-grub, then check the firmware boot menu.

Step	Action	Applies To
1	Back up files to external/cloud storage	Windows
2	Save BitLocker key, then turn BitLocker off	Windows
3	Shrink C: via Disk Management	Windows
4	Turn off Fast Startup	Windows
5	Leave Secure Boot on	Windows/UEFI
6	Create bootable USB with Rufus	Windows
7	Boot USB in UEFI mode	Firmware
8	Install alongside Windows Boot Manager	Ubuntu installer
9	Choose OS at GRUB menu	Ubuntu/Windows

Resources

• Install Ubuntu desktop (official tutorial)
• Ubuntu Desktop download
• Windows 11 release information
• Turn off BitLocker in Windows (Ubuntu documentation)
• Disk Management in Windows